References of "Verlinden, Bert"
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See detailTransient yielding during compression tests on ECAP’ed AA1050 Aluminium
Verlinden, Bert; Chen, Enze; Duchene, Laurent ULg et al

in Materials Science Forum (2011), 667-669

In most papers dealing with tension and/or compression tests, the conventional yield stress is determined either by an offset method (usually 0.2% strain) or by back extrapolation from the stress-strain ... [more ▼]

In most papers dealing with tension and/or compression tests, the conventional yield stress is determined either by an offset method (usually 0.2% strain) or by back extrapolation from the stress-strain curve. In our experiments on ECAP‟ed Aluminium a transient hardening saturation (THS) is always observed during the compression tests, but not during the tensile tests. This THS occurs at a significantly lower stress than the conventional yield stress. The aim of the present paper is to determine which the “real” start of yielding is. Two different experimental approaches have been adopted, confirming that the THS stage is exactly the yielding stage. This is not unimportant because it increases the tension-compression asymmetry and hence the back-stress and kinematic hardening. The reason for this different behaviour between tension and compression can be ascribed to a different change in strain path with respect to the ECAP deformation. [less ▲]

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See detailPrediction of the Tension/Compression asymmetry of ECAP processed FCC material using an integrated model based on dislocation and back-stress
Chen, Enze; Duchene, Laurent ULg; Habraken, Anne ULg et al

in Materials Science Forum (2011), 667-669

In our recent work, a new integrated model was proposed to describe the back-stress evolution based on the dislocation substructure and texture. By relating the back-stress to the dislocation density in ... [more ▼]

In our recent work, a new integrated model was proposed to describe the back-stress evolution based on the dislocation substructure and texture. By relating the back-stress to the dislocation density in cell walls and in the cell interior, this model is able to capture the back-stress evolution of ECAP processed pure aluminium. In this paper, the model is used for another FCC material, namely copper. The aim is to check whether this model is able to predict the tension/compression asymmetry (due to the back-stress) of copper. The results show that this is indeed the case and it is also found that the strain rate ratio proposed in our previous work [1] is a function of the dislocation density ratio. [less ▲]

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See detailModelling compression tests on aluminium produced by equal channel angular extrusion
Poortmans, Stijn; Duchene, Laurent ULg; Habraken, Anne ULg et al

in Acta Materialia (2009)

The main objective of this paper was to characterize the mechanical properties of commercial purity aluminium AA1050 after being submitted to the equal channel angular extrusion (ECAE) process ... [more ▼]

The main objective of this paper was to characterize the mechanical properties of commercial purity aluminium AA1050 after being submitted to the equal channel angular extrusion (ECAE) process. Compression tests on cylindrical samples extracted from ECAE material are extensively described. The influence of ECAE conditions (number of passes, route, etc.) on the mechanical response is assessed. The extraction of the material behaviour from the experimental results is not straightforward because of inhomogeneities occurring during the test. Therefore, an inverse modelling with the finite element method was used to obtain accurate material parameters by optimization. It appeared that an accurate material yield locus (based on texture analysis) is necessary in order to reproduce the anisotropic behaviour of the ECAE material. On the other hand, its hardening behaviour during compression tests was satisfactorily represented by an elastic (near) perfectly plastic model. [less ▲]

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See detailMultiscale modeling of equal channel angular extruded aluminium with strain gradient crystal plasticity and phenomenological models
Duchene, Laurent ULg; Geers, M. G. D.; Brekelmans, W. A. M. et al

in Rollett, A. (Ed.) Proceedings of the 15th International Conference on the Texture of Materials (ICOTOM-15) (2008)

The Equal Channel Angular Extrusion process is used to modify the microstructure of an AA1050 aluminum alloy in order to produce an ultra fine grained material. Due to the severe plastic deformation ... [more ▼]

The Equal Channel Angular Extrusion process is used to modify the microstructure of an AA1050 aluminum alloy in order to produce an ultra fine grained material. Due to the severe plastic deformation undergone by the material during the ECAE process, the subsequent behavior of the material is non-conventional and difficult to model with classical constitutive laws (e.g. ECAE aluminum presents a large initial back-stress which must be adequately incorporated in the model). In this study, the evolution of the back-stress during the ECAE process is analyzed. Two different numerical models were investigated in this respect. The first one is a single crystal strain gradient plasticity model based on dislocation densities. The second model is the Teodosiu and Hu’s hardening model, which is a microstructuraly based phenomenological model at the macroscale. The results provided by the two models are obviously distinct. Nevertheless, some common trends can be pointed out, among which the amplitude of the back-stress that is similar. In agreement with the cyclic deformation mode of the studied route C ECAE process, the evolution of the predicted back-stress is also cyclic in both models. [less ▲]

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See detailCorrecting tensile test results of ECAE-deformed aluminium
Poortmans, Stijn; Boubakar, Diouf; Habraken, Anne ULg et al

in Scripta Materialia (2007), 56(9), 749-752

Performing tensile tests on ECAE material reveals a long post-uniform elongation. In order to calculate correct true stress–true strain diagrams, three different approaches are used: measurements of the ... [more ▼]

Performing tensile tests on ECAE material reveals a long post-uniform elongation. In order to calculate correct true stress–true strain diagrams, three different approaches are used: measurements of the actual sample geometry, a neck evolution model proposed by Segal [V.M. Segal, S Ferrasse, F. Alford, Mater. Sci. Eng. A442 (2006) 321–326] and an inverse modelling method by finite element (FE) simulations. [less ▲]

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See detailInhomogeneous and anisotropic deformation behavior and strain hardening of ultrafine-grained aluminium by ECAP
Poortmans, Stijn; El Houdaigui, Fouad; Habraken, Anne ULg et al

in Zhu, Y. T.; Langdon, T. G.; Horita, Z. (Eds.) et al Proceedings of the Ultrafine Grained Materials IV Conference (2006)

Hot-rolled AA1050 commercial pure aluminum was deformed by ECAP (Equal Channel Angular Pressing) at room temperature following route BC for 8 passes. Mechanical testing at room temperature on both hot ... [more ▼]

Hot-rolled AA1050 commercial pure aluminum was deformed by ECAP (Equal Channel Angular Pressing) at room temperature following route BC for 8 passes. Mechanical testing at room temperature on both hot-rolled aluminum and aluminum after ECAP consisted of uniaxial tension, axisymmetric compression and shear by torsion. The phenomenological Hill’s criterion identified from texture data accounts for the observed tension-compression asymmetry due to ECAP and predicts torsion yielding close to measurements. FE simulations of the compression tests are performed with a Hill model or a Minty micro-macro model and coupled with an isotropic Voce saturation hardening law. These simulations compute the inhomogeneous behavior due to barreling, the observed sample anisotropy and the force-displacement curve. Comparisons of numerical and experiments results provide a first identification of the hardening parameters and the friction coefficient during compression tests. [less ▲]

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See detailA phenomenological model to simulate mechanical tests on ultrafine-grained aluminium produced by ECAE
Diouf, Boubakar; El Houdaigui, Fouad; Poortmans, S. et al

in Mota Soares, C. A. (Ed.) Proceedings of the III European Conference on Computational Mechanics Solids (ECCM III) (2006)

Results of FEM simulations predicting the mechanical behavior at room temperature of test specimens of ultrafine-grained aluminum produced by ECAE are presented. The constitutive law is either based on a ... [more ▼]

Results of FEM simulations predicting the mechanical behavior at room temperature of test specimens of ultrafine-grained aluminum produced by ECAE are presented. The constitutive law is either based on a Hill model or on the Minty micro-macro model and coupled with an isotropic hardening law and/or kinematic hardening law. The yield locus shape, its size and its position during tension, compression and torsion tests have been studied. Initial texture measurements allow the identification of a constitutive law based on a set of representative crystals and crystal plasticity approach using a Full- Constraint Taylor model. Finite element simulations using the previous constitutive laws are compared with experimental investigations. The results show that applying an initial back stress identified by tensile and compression tests to the yield locus predicts the initial flow stress in torsion test. The Minty micro-macro model coupled with a Voce type hardening model gives a good agreement with experimental results for the prediction of the shape at different stages of deformation of a compressed test specimen. The simulation of tensile tests underline the need of inverse modeling as, due to the test specimen shape, the test is far from being homogeneous. The link between test specimen length and the necking appearance is studied. [less ▲]

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See detailAnisotropic yield locus of ultrafine-grained aluminium produced by Equal Channel angular extrusion
El Houdaigui, Fouad; Duchene, Laurent ULg; Habraken, Anne ULg et al

in Onate, E.; Owen, D. R. J. (Eds.) Proceedings of the VIII International Conference on Computational Plasticity (COMPLAS VIII) (2005)

Macroscopic tensile, compression and torsion tests have been performed as well as texture measurements. Based on these data a phenomenological yield locus has been defined to describe the behaviour of an ... [more ▼]

Macroscopic tensile, compression and torsion tests have been performed as well as texture measurements. Based on these data a phenomenological yield locus has been defined to describe the behaviour of an ultrafine-grained aluminum obtained by ECAE. [less ▲]

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See detailThe Developments of Cold-rolled TRIP-assisted Multiphase Steels. Al-alloyed TRIP-assisted Multiphase Steels
Jacques, Pascal J.; Girault, Etienne; Mertens, Anne ULg et al

in ISIJ International (2001), 41(9), 1068-1074

The influence of heat-treating conditions on the retention of carbon-enriched austenite of TRIP-assisted multiphase steel grades containing different amounts of silicon and/or aluminium is investigated ... [more ▼]

The influence of heat-treating conditions on the retention of carbon-enriched austenite of TRIP-assisted multiphase steel grades containing different amounts of silicon and/or aluminium is investigated. The ensuing mechanical properties resulting from the TRIP effect are also scrutinised. The bainite transformation kinetics was followed by dilatometry whereas a detailed characterisation of the microstructures led to the construction off transformation maps giving the volume fractions of the different phases and the carbon content of the austenite. The role of silicon and aluminium additions (i)on the retention of austenite by partial bainite transformation and (ii) on the mechanical properties is enlightened. A strong influence of the solid-solution strengthening effect of silicon is highlighted. Aluminium seems to be an effective alloying element for the retention of austenite in TRIP-aided steels even if lower strength levels can be attained. A mixed Al-Si TRIP-aided steel seems to be a very good compromise between the processing needs, the required mechanical properties and the industrial constraints. [less ▲]

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See detailComparison of the effects of silicon and aluminium on the tensile behaviour of multiphase TRIP-assisted steels
Girault, Etienne; Mertens, Anne ULg; Jacques, Pascal J. et al

in Scripta Materialia (2001), 44

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